libstdc++: Fix constraints on std::optional comparisons [PR 96269]

The relational operators for std::optional were using the wrong types
in the declval expressions used to constrain them. Instead of using
const lvalues they were using non-const rvalues, which meant that a type
might satisfy the constraints but then give an error when the function
body was instantiated.

libstdc++-v3/ChangeLog:

	PR libstdc++/96269
	* include/std/optional (operator==, operator!=, operator<)
	(operator>, operator<=, operator>=): Fix types used in
	SFINAE constraints.
	* testsuite/20_util/optional/relops/96269.cc: New test.

diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index f9f42efe09ce2deff3ec22ed435cbb6b91e4504a..5ea5b39d0e692a6af6e4c8dc739c8c83ab8e628d 100644 (file)
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1002,11 +1002,41 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     using __optional_relop_t =
       enable_if_t<is_convertible<_Tp, bool>::value, bool>;
 
+  template<typename _Tp, typename _Up>
+    using __optional_eq_t = __optional_relop_t<
+      decltype(std::declval<const _Tp&>() == std::declval<const _Up&>())
+      >;
+
+  template<typename _Tp, typename _Up>
+    using __optional_ne_t = __optional_relop_t<
+      decltype(std::declval<const _Tp&>() != std::declval<const _Up&>())
+      >;
+
+  template<typename _Tp, typename _Up>
+    using __optional_lt_t = __optional_relop_t<
+      decltype(std::declval<const _Tp&>() < std::declval<const _Up&>())
+      >;
+
+  template<typename _Tp, typename _Up>
+    using __optional_gt_t = __optional_relop_t<
+      decltype(std::declval<const _Tp&>() > std::declval<const _Up&>())
+      >;
+
+  template<typename _Tp, typename _Up>
+    using __optional_le_t = __optional_relop_t<
+      decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>())
+      >;
+
+  template<typename _Tp, typename _Up>
+    using __optional_ge_t = __optional_relop_t<
+      decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>())
+      >;
+
   // Comparisons between optional values.
   template<typename _Tp, typename _Up>
     constexpr auto
     operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() == declval<_Up>())>
+    -> __optional_eq_t<_Tp, _Up>
     {
       return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
             && (!__lhs || *__lhs == *__rhs);
@@ -1015,7 +1045,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, typename _Up>
     constexpr auto
     operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() != declval<_Up>())>
+    -> __optional_ne_t<_Tp, _Up>
     {
       return static_cast<bool>(__lhs) != static_cast<bool>(__rhs)
        || (static_cast<bool>(__lhs) && *__lhs != *__rhs);
@@ -1024,7 +1054,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, typename _Up>
     constexpr auto
     operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() < declval<_Up>())>
+    -> __optional_lt_t<_Tp, _Up>
     {
       return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
     }
@@ -1032,7 +1062,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, typename _Up>
     constexpr auto
     operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() > declval<_Up>())>
+    -> __optional_gt_t<_Tp, _Up>
     {
       return static_cast<bool>(__lhs) && (!__rhs || *__lhs > *__rhs);
     }
@@ -1040,7 +1070,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, typename _Up>
     constexpr auto
     operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() <= declval<_Up>())>
+    -> __optional_le_t<_Tp, _Up>
     {
       return !__lhs || (static_cast<bool>(__rhs) && *__lhs <= *__rhs);
     }
@@ -1048,7 +1078,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, typename _Up>
     constexpr auto
     operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() >= declval<_Up>())>
+    -> __optional_ge_t<_Tp, _Up>
     {
       return !__rhs || (static_cast<bool>(__lhs) && *__lhs >= *__rhs);
     }
@@ -1134,73 +1164,73 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, typename _Up>
     constexpr auto
     operator==(const optional<_Tp>& __lhs, const _Up& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() == declval<_Up>())>
+    -> __optional_eq_t<_Tp, _Up>
     { return __lhs && *__lhs == __rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator==(const _Up& __lhs, const optional<_Tp>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Up>() == declval<_Tp>())>
+    -> __optional_eq_t<_Up, _Tp>
     { return __rhs && __lhs == *__rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator!=(const optional<_Tp>& __lhs, const _Up& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() != declval<_Up>())>
+    -> __optional_ne_t<_Tp, _Up>
     { return !__lhs || *__lhs != __rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator!=(const _Up& __lhs, const optional<_Tp>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Up>() != declval<_Tp>())>
+    -> __optional_ne_t<_Up, _Tp>
     { return !__rhs || __lhs != *__rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator<(const optional<_Tp>& __lhs, const _Up& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() < declval<_Up>())>
+    -> __optional_lt_t<_Tp, _Up>
     { return !__lhs || *__lhs < __rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator<(const _Up& __lhs, const optional<_Tp>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Up>() < declval<_Tp>())>
+    -> __optional_lt_t<_Up, _Tp>
     { return __rhs && __lhs < *__rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator>(const optional<_Tp>& __lhs, const _Up& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() > declval<_Up>())>
+    -> __optional_gt_t<_Tp, _Up>
     { return __lhs && *__lhs > __rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator>(const _Up& __lhs, const optional<_Tp>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Up>() > declval<_Tp>())>
+    -> __optional_gt_t<_Up, _Tp>
     { return !__rhs || __lhs > *__rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator<=(const optional<_Tp>& __lhs, const _Up& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() <= declval<_Up>())>
+    -> __optional_le_t<_Tp, _Up>
     { return !__lhs || *__lhs <= __rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator<=(const _Up& __lhs, const optional<_Tp>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Up>() <= declval<_Tp>())>
+    -> __optional_le_t<_Up, _Tp>
     { return __rhs && __lhs <= *__rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator>=(const optional<_Tp>& __lhs, const _Up& __rhs)
-    -> __optional_relop_t<decltype(declval<_Tp>() >= declval<_Up>())>
+    -> __optional_ge_t<_Tp, _Up>
     { return __lhs && *__lhs >= __rhs; }
 
   template<typename _Tp, typename _Up>
     constexpr auto
     operator>=(const _Up& __lhs, const optional<_Tp>& __rhs)
-    -> __optional_relop_t<decltype(declval<_Up>() >= declval<_Tp>())>
+    -> __optional_ge_t<_Up, _Tp>
     { return !__rhs || __lhs >= *__rhs; }
 
 #ifdef __cpp_lib_three_way_comparison

diff --git a/libstdc++-v3/testsuite/20_util/optional/relops/96269.cc b/libstdc++-v3/testsuite/20_util/optional/relops/96269.cc
new file mode 100644 (file)
index 0000000..2054d36
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/optional/relops/96269.cc
@@ -0,0 +1,76 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <optional>
+
+struct X
+{
+  template <typename T>
+    bool operator==(const T&) /* not const */ { return false; }
+
+  template <typename T>
+    bool operator!=(const T&) /* not const */ { return false; }
+
+  template <typename T>
+    bool operator<(const T&) /* not const */ { return false; }
+
+  template <typename T>
+    bool operator>(const T&) /* not const */ { return false; }
+
+  template <typename T>
+    bool operator<=(const T&) /* not const */ { return false; }
+
+  template <typename T>
+    bool operator>=(const T&) /* not const */ { return false; }
+};
+
+void test01()
+{
+  // PR 96269 optional comparison with nullopt fails
+  std::optional<X> x;
+  bool eq [[maybe_unused]] = std::nullopt == x;
+
+  bool ne [[maybe_unused]] = std::nullopt != x;
+  bool lt [[maybe_unused]] = std::nullopt <  x;
+  bool gt [[maybe_unused]] = std::nullopt >  x;
+  bool le [[maybe_unused]] = std::nullopt <= x;
+  bool ge [[maybe_unused]] = std::nullopt >= x;
+}
+
+template<typename T>
+  concept optional_lt_cmp
+    = requires(std::optional<T> o, T t) { { o < t } -> std::same_as<bool>; };
+
+template<typename T>
+  concept optional_gt_cmp
+    = requires(std::optional<T> o, T t) { { o > t } -> std::same_as<bool>; };
+
+template<typename T>
+  concept optional_le_cmp
+    = requires(std::optional<T> o, T t) { { o <= t } -> std::same_as<bool>; };
+
+template<typename T>
+  concept optional_ge_cmp
+    = requires(std::optional<T> o, T t) { { o >= t } -> std::same_as<bool>; };
+
+static_assert( ! optional_lt_cmp<X> );
+static_assert( ! optional_gt_cmp<X> );
+static_assert( ! optional_le_cmp<X> );
+static_assert( ! optional_ge_cmp<X> );